Filter by form is null/not null

[lynn atkinson]

I have a database which is split in to front and back end.
It is also linked to certain tables in another database eg
to get employee name and address etc. When I enter Filter
by Form mode to search for anything in the form, all I get
under the drop down is "is null" or "is not null".
Why do I not get to select from the contents of these
fields? and how do I display the contents of the fields?

Any help appreciated